The present invention relates to a structure of a magneto-resistive head, and in particular to a head structure suitable for decreasing the drop in the S/N ratio which is caused by external noises superimposed over the reproduced signals when signals are read out.
Densities of magnetic recording units have been increased more and more. As heads for realizing such recording units, thin film heads with the thin film technique applied thereto have been brought into use. Among these thin film heads, a magneto-resistive head for multitrack (hereafter referred to as MR head) utilizing the magneto-resistive effect of a ferromagnetic thin film advantageously provides a high level output despite its high recording density, because its reproduced output does not depend on the relative speed between the recording medium and the magnetic head, but depends only upon the magnitude of the signal magnetic field caused by the recording medium. The MR heads are being applied to magnetic recording units in various fields as reproducing heads.
The general structure of the MR head is disclosed in Japanese Patent Unexamined Publication No. 50-59023. On a base plate 1, a pair of magnetic shield layers 6,7 are provided on both side faces of an MR element 2 via thin isolation layers 8,9 as illustrated in FIG. 2. A conductor layer 5 for allowing flow of a drive current into the MR element and for taking out a reproduced signal from the MR element is connected to the MR element 2. The magnetic shield layers 6,7 are provided to shield an unnecessary part of the signal magnetic field caused by the recording medium, which part is sensed by the MR element 2 but is not needed. Thus the frequency characteristics of the reproduced signal is improved and the resolution is increased by including these magnetic shield layers 6 and 7.
In such a structure, however, spike noises are caused if a recording medium which is an isolator runs in a narrow gap facing the head surface. When the information is reproduced, such spike noises lower the signal to noise ratio and cause reproduction errors.